Composites are attractive to the aerospace industry because of their high strength, high rigidity, and low weight. A composite structure such as skin or a stiffener may be constructed by stacking up plies of resin-infused carbon fiber tape or fabric on a mandrel, forming an air-tight envelope over the ply stack-up, and curing the stack-up.
Weight reduction in an aircraft is highly desirable, as it reduces aircraft operating costs. The weight of composite aircraft parts may be reduced by using composite material where needed. Skin may be formed from an outer ply. Pad-ups on the skin may be used to increase thickness at locations where fasteners will be installed or extra strength is needed. In a complex structure such as a composite fuselage, the skin may have an overall nominal thickness, which is padded up to various degrees over arbitrary areas for strength or gage.
A ply stack-up may have a step-like geometry. Prior to curing, edges of the ply stack-up are sharp. During curing, pre-impregnated resin flows through the stack-up, forming ramps off the edges, which transition from one ply to the next. A complex structure such as a fuselage may have tens of thousands of edges.
In the aircraft industry, it is useful to model the geometry of composite parts. The geometric model may be used to determine material properties (e.g., stresses, strains, and displacement) for the composite parts, generate tape laying sequences, and create automated NC part programs.